For joining two pieces of boarding together so that an edge of one piece abuts a face of the other piece, it is common practice to join them using dowels, that is to say, pegs, each of which extends into its own hole in the edge of said one piece and, traversing the joint, also into a corresponding hole in the face of the other piece. It is virtually essential to use a jig of some kind in order to obtain accurate alignment of the dowel holes. However, most or all known jigs for this purpose are expensive and complicated.